The present invention relates to a vacuum cartridge designed to break an electrical circuit in a medium voltage circuit breaker or switch, as well as a switch incorporating such a cartridge.
An electrical switch with a vacuum cartridge is already known described in U.S. Pat. No. 5,155,315, mainly comprising a sealed enclosure filled with a high dielectric strength gas, in which a vacuum cartridge is arranged containing a pair of arcing contacts, one stationary and the often movable, a pair of main contacts electrically connected in parallel to the arcing contacts, and an operating mechanism connected to the contacts to open the arcing contacts after the main contacts, and to close the arcing contacts before the main contacts. The two above-mentioned arcing contacts each comprise a disk-shaped contact part. The stationary contact is securely fixed to one of the end-plates of the enclosure whereas the movable contact is slidably mounted in the other of the two end-plates of the enclosure and is connected to the operating mechanism in order to achieve breaking of the electrical circuit.
Although the above-described vacuum cartridge is satisfactory in a general sense, it does nevertheless have certain drawbacks. For example, when closing of the contacts takes place, the two disks are rarely exactly parallel to one another. It is therefore difficult to obtain an immediate contact over the whole surface of the disks, thereby concentrating the electrical arc at the circumference of the disks, and reducing the breaking capacity. Another drawback is that the force required to maintain contact between the two disks is great and requires the use of a consequent operating mechanism.